1. Field Of The Invention
The field of the invention is automatic range changing or selecting circuits for use with an amplifier having a high gain. Such circuits are useful for automatically changing the measuring range in a spectrofluorometer utilizing a photomultiplier tube linear microphotometer.
2. Description Of The Prior Art
Heretofore various automatic range changing or range selecting circuits have been proposed and examples of such circuits can be found in the following U.S. Pat. Nos.:
3,539,936 PA1 3,579,138 PA1 3,711,774 PA1 3,742,354 PA1 3,828,262 PA1 3,926,819 PA1 3,947,806
The automatic range selection circuit of the present invention, hereinafter described in detail, provides for easy and fast determination of a unknown output signal strength from a sensing circuit such as a photomultiplier tube. The automatic range selection circuit of the present invention has a number of advantages, many of which provide improvements over previously proposed automatic range changing circuits. Some of these advantages are as follows.
1. The automatic range selection circuit of the present invention has fewer electronic components than many of the previously proposed automatic range changing circuits.
2. The automatic range selection circuit of the present invention has incorporated therein by reason of the circuit elements and connections thereof hereinafter described in detail, automatic filtering whereby ranges are not switched on short noise spikes.
3. The automatic range selection circuit of the present invention will switch to a higher or lower range as necessary whereas many of the previously proposed automatic range changing circuits only scan ranges in one direction.
4. The circuit components and their connections in the automatic range selection circuit of the present invention can be easily changed or adjusted for the speed of the principal amplifier of the circuit whereby the automatic range selection circuit can be used with very fast or ultra slow time constants.
5. THE AUTOMATIC RANGE SELECTION CIRCUIT OF THE PRESENT INVENTION IS ESSENTIALLY AN ANALOG CIRCUIT AND DOES NOT UTILIZE CLOCKS OR OTHER DIGITAL CIRCUITS UTILIZED IN MANY PREVIOUSLY PROPOSED AUTO RANGE CHANGING CIRCUITS. As a result, EMI problems which arise from the coupling of digital circuits to sensitive analog circuits are not incurred with the automatic range selection circuit of the present invention.
Other advantages of the range selection circuit of the present invention will be apparent from the description of the preferred embodiment of the invention set forth below.